With the massive success of Left 4 Dead came the pressure to do a sequel, and howls of protest at the sequel coming so soon. Valve Software has never made a third installment of any franchise, so this may very well be the last. The community was hoping for a lot more time to have passed, to allow for much more advancement of the Source engine with which they script games before closing out such a wonderful world.
But they did make quite a few improvements, and it shows in the world they created. Now wounds on zombies aren't pasted on as graphical elements, "chunks" are torn out of the models themselves, making injuries far more gruesome. Algorithms for zombie and car generation are far more efficient, leading to way more variations and less homogenous looking hordes.
New zombie specials were created, and melee weapons were introduced, allowing you to brain zombies with anything from a cricket bat to a chainsaw. Sample vials of Boomer vomit can be found and thrown, leading to zombies attacking whatever's been hit with it, or just a section of wall or floor. In addition to pain pills you can also find adrenaline shots which make you do things faster (and win a "strongman" bell-ringing contest if you hit the target with a melee weapon while on it). You can also carry, in place of a health kit, a defibrillator which will return a recently-killed Survivor back to life.
The rich motion captures of stuntmen doing shambling, vomiting and such were augmented, and the texture rendering was improved.
The intro video to Left 4 Dead 2 keys off what you knew from Left 4 Dead but shows the new characters and situations and specials you'll end in. As opposed to a linear episode, it shows snippets of the various campaigns to come in a "movie trailer" format, playing off the "you're in a movie" feel of the campaign presentations. Once again, you can play these in any order, but the intro video ends with the beginning of Dead Center, showing it to be the first in the series chronologically.
There are four new characters: "Coach" is a middle aged African American portly ex-linebacker who went from college player and NFL hopeful to teaching in a rural Georgia school (and is voiced by an actor who went on to be in The Walking Dead). Rochelle was an associate news producer when things went south, and fast, and is a young black female in a Depeche Mode T-shirt. We're not sure about Nick's background, except that he looted himself a really nice and expensive white suit as soon as the cops lost control, and muses that he probably shouldn't be in possession of weapons, as a felon. The cast is rounded out by young buck 'good ol' boy' Ellis, whose off-topic ramblings and goofy outbursts add a badly needed levity to the proceedings.
The voice acting experiments of Left 4 Dead were expanded in this game. There is a rich vocabulary of sentences which are chosen by the AI to string together a somewhat coherent conversation here and there. If a player is injured, another tells him or her to "heal up". The director remembers which sentences were used and chooses others to go with so that you don't hear the same things over and over, and natural, organic-sounding responses follow play action. This has been further enhanced in Left 4 Dead 2, to allow for customizable/non-repeatable intros to DLC campaigns, and even more realistic interaction.
If played in chronological order, the intro movie showing Coach complaining about the flights of stairs it's taking to get to the roof to meet up with the Army and to get evacuated ends with the four watching in complete horror as the very last of the helicopters fade into the clouds. All evacuations are out, and those left behind are truly left for dead, and it segues into the rooftop intro to "Dead Center". The four meet on the rooftop of a hotel in Savannah, Georgia and have to fight their way back down through the hotel (which is on fire), through some abandoned highways and a redneck gun store, finally ending up in a mall. Ellis hits on the idea of using a 1969 Dodge Charger that was an attraction to the mall before the plague struck, being the possession and main ride of NASCAR driver "Jimmy Gibbs Jr." (there is a one in one thousand chance of actually seeing zombified Jimmy Gibbs Jr.). Noting that stock cars are empty of gas until used, the final part of this game involves scavenging ten gas cans in the mall, before Ellis, true to his "Dukes of Hazzard" persona roars that muscle car out of the mall, straight through the plate glass doors.
The story continues in the DLC campaign "The Passing". Stuck at an upraised bridge, the four new survivors meet three of the original Left 4 Dead survivors who are resting at the top of the bridge after the events of "The Sacrifice". Showing off the new scriptability of dialogue in the new engine, either Ellis is bashfully stammering at new love interest Zoey, or Nick is threatening Francis, or Louis is explaining with his broken leg they can't help right now (these and other random scenario starters kick off the episode). But the four can lower the bridge and let the car pass if the four can make their way through the underground tour to the other side of the river, and restart the generators. Fighting their way through the town, they go under the river and end up in the same finale location as "The Passing". There are two main differences though - the first being that you need to scavenge fuel in gas cans to refuel the generator before starting it, and the corpse of Bill, lying against some pipework near the generator where he made his last stand. Fueling the generator generates hordes and Tanks, and eventually Francis and Zoey make their way to a nearby rooftop to help add firepower to your team's. Once the bridge is down you make your way to your car to complete the level, and if you started with Ellis bashfully unable to talk to Zoey, it ends with her calling out to him, too late, to see if he'll join them, demonstrating that his affection was returned.
Moving along to the disc campaigns, the end of the road in "Dark Carnival" is Highway 16 between Savannah and Atlanta, Georgia. Ellis doesn't really want to leave the car, but with the roads made unpassable by a severe pile-up, they say goodbye to the Charger and head off on foot. Noting searchlights, they make their way through a ruined hotel and out to "Whispering Oaks", a fairground that is reminiscent of the finale of the movie Zombieland, also produced in Georgia. Fighting through the fairground, potentially rescuing a garden gnome, Coach hits on an idea. A helicopter has been flying around and if they can get its attention, maybe it will rescue them. Making their way into a stadium attached to the fairgrounds, they start the lightshow and fireworks display and rock concert that was supposed to be put on by the "Midnight Riders", a clear nod to Lynyrd Skynyrd and other Southern Rockers - especially with Coach's joke "I have all their albums, even the new ones that aren't any good." The ensuing lightshow attracts hordes and Tanks, but also the helicopter, and you barely make it onto the helicopter to escape.
Everyone is complaining at Nick in "Swamp Fever", which is probably in Mississippi. He shot the pilot, just as how Zoey shot the pilot from "No Mercy" in the first Left 4 Dead. Nick points out ruefully that he wasn't a very good pilot once he turned into a zombie. They're in a swamp. This is probably the very best use of the new milieu in the series: whereas the first Left 4 Dead was about urban claustrophobia and having to "get out", they're now "out", but to what end - showing mile after mile of abandoned ruin shows the existential horror of a post-apocalypse. Making their way through barely-habitable shotgun shacks and across a river on a noisy ferry-raft, they eventually make their way (with a stunning, stunning "looking into the sun at dawn through the mist" atmosphere effect) through to a plantation house where they encounter a radio manned on the other side by a Cajun in a fishing vessel. He offers to come pick them up, but they have to hold on and survive til he gets there.
Virgil, the NPC Cajun boat capitain, is unable to continue much further without fuel, so the team volunteers in "Hard Rain" to get more fuel. Thinking it just a matter of going just up the street, they realize to their chagrin that the gas station is out of fuel, and they'll have to go much further inland through tons of zombies to find some. They also are lucky that the burger joint they land at has weapons, because they forgot their guns and the flares to signal Virgil to come back (he went into the river for safety). They fight their way through the riverside town, and then through an abandoned sugar mill full of Witches, only to find their progress impeded by violent, sudden summer storms common in the Deep South. Making their way to another gas station, they suit up with a container of diesel each, and then fight their way back, signalling Virgil with the Burger Joint sign, which also alerts every zombie in the area.
In "The Parish", Virgil sets them off at their destination, New Orleans, Louisiana. They are in a not-quite accurate but similar-enough-in-feel version of the French Quarter to make their way through the market, and through the Quarter itself into the Necropoli of the above ground cemeteries. As they get closer to the very, very last evacuation point still standing, the Army and Air Force are bombing the city, shaking the foundations of all the buildings and causing the characters to scream with rage at the military. Arriving at the bridge, they make contact with the military via a dead soldier's walkie-talkie. If they can get across the bridge soon, they'll be safe, but they're just about to blow up the bridge itself, so they had better hurry. Reaching the other side of the bridge, they barely make it to the last military helicopter standing by waiting for them to tumble into the back, before the whole series ends in the thunderous explosion of the bridge into New Orleans.
The feel of this installment is one of a more existential dread. It's one thing to be in what appears to be a shelled-out city, and it's another to see entropy and decay pull a curtain over the remnants of a society. Similar to the intro to the TV version of The Walking Dead, Left 4 Dead 2 is more open as a set-piece, but far more depressing. Sure you can run, you have any of a number of open fields to run in, but you're going to run out of ammo. You're going to run into thickets, bushes where you can't see the Witch sobbing in the darkness. You can see them a mile away, but they can see you a mile away, also. And everything you come across, from a panicked car pile-up to abandoned buildings reminds you that everything is dead and gone.
There are also new threats in this game: the "Charger" is a giant-right-armed charging zombie that grabs the closest survivor in a charge and slams him or her repeatedly against the floor, helpless and losing life fast, until rescued. To prevent clumping and camping, a "Spitter" discarges an acid-vomit that will rapidly incap anyone staying in the pool of bubbling green liquid. A "Jockey" is a spindly, hyperactive gibbering monster that latches on to a survivor and steers him or her away from friends and safety and into hazards such as acid vomit, a Boomer's path, flames, or into a Witch. The designs of the Boomer and the Witch also have variants: there is a female Boomer as well, and a "wandering Witch" who walks around sobbing into her hands.
There's also "uncommon infected" in this game, infected who aren't like the other zombies. One unique one is the "Jimmy Gibbs Jr" zombie, but there are hazmat suit wearing "CEDA" agents (an expy of the CDC and FEMA) who will occasionally drop vials of Boomer puke. There are "mudmen", swamp zombies on all fours who splatter you with mud when dispatched. Bulletproof zombies exist with zombified riot police, who can only be killed by being shot in the back. In the level at the fairground, there are zombie clowns whose noses "honk" when hit with weapons, and who need to be killed because their squeaking shoes attract hordes. In "Hard Rain" there are ex-workers with hearing protection who won't chase pipe bombs. In the DLC "The Passing" there are "fallen survivors", zombified ex-Survivors carrying anything from health kits to weapons. In passing, stealing 10 vials of Boomer vomit from fallen CEDA workers nets you the achievement "Robbed Zombie". You have to appreciate that kind of cleverness.
The music has also been awesomely retuned: everything from being "covered" as a haunting dobro and harmonica theme, to being picked out as banjo riff with a rumbling bass pad, to being echoed as a second line brass band tune in New Orleans. Jukeboxes also have randomly available songs, from two pieces by the "Midnight Riders" to an alt-rock song about having become zombified, all we want to do is eat your brains (on the word "brains" a zombie horde attacks).
With the purchase of the ascended canon "Cold Stream" campaign, you get the bonus of having upgraded versions of all Left 4 Dead campaigns. So if you only want to purchase one of the two games, with the purchase of "Left 4 Dead 2" and the "Cold Stream" DLC for $6.99, you get the original levels of Left 4 Dead as well. They have been upgraded, re-rendered with a better engine, tighter models, the inclusion of the new Special infected, and melee weaponry.
There are rumors of Left 4 Dead 3 possibly being the showcase for the new version of the Source 3 engine. If this is the case, it would be the very first "3" of a game Valve has ever produced, even if it's the same content from before but issued with newer technology. That being said, whether the end or not, Left 4 Dead 2 is the culmination and triumph of a well thought out, well executed genre survival horror game. It's a tour de force, constantly being expanded with user generated content. But let's hope that the franchise still has legs, and that Nick's prouncement in the intro video proves true: "I have not... come this far..... to die now."